1. FIELD OF THE INVENTION
The present invention relates to a titanium-tungsten (Ti-W) target material used for forming or otherwise making a barrier metal layer used in a semiconductor device, and to a manufacturing method therefor.
2. DESCRIPTION OF THE RELATED ART
As the degree of integration of LSIs has increased in recent years, the migration of aluminum (Al) has become a problem which is caused by a mutual diffusion in a contact portion between aluminum wiring and a semiconductor substrate of silicon. As a countermeasure for such a problem, the insertion of a barrier metal layer into the space between the aluminum wiring and the silicon substrate has been under investigation.
A thin titanium-tungsten film (typically composed of 10 wt% of titanium and the balance of tungsten) is often used as a barrier metal layer. A method of sputtering a target is employed as a method of forming such a thin titanium-tungsten film.
In general, a titanium-tungsten target material for the thin film is manufactured by blending and hot-pressing of tungsten powder and titanium powder.
Since the oxygen content of the titanium powder serving as a raw material of the conventional titanium-tungsten target is high, only targets having a high oxygen content are obtained.
In such a target material having a high oxygen content, oxygen is liberated while sputtering is performed, thus causing undesirable problems, such as cracks of the target, oxidation of formed films, and variations in the film quality.
U.S. Pat. No. 4,838,935 discloses a method of reducing the oxygen content of such a titanium-tungsten target. In this document, a titanium-tungsten target material with its carbon and oxygen contents reduced can be obtained at high density and a low void content. The titanium-tungsten target material can be obtained by replacing at least a portion of titanium powder with hydrogenated titanium, by employing a hydrogenated titanium powder and a tungsten powder having a distribution of a binodal grain diameter, or by employing the hydrogenated titanium powder and a mixture of a titanium powder.
JP-A-63-303017 also discloses a method of reducing the oxygen content of a titanium-tungsten target. In this method, a tungsten powder and a hydrogenated titanium powder are blended together and hot-pressed after or while both powders are dehydrogenated.
The use itself of the hydrogenated titanium powder is effective in preventing oxidation and also in reducing a pickup of oxygen when the hydrogenated titanium powder is pulverized because it can be pulverized more readily than an ordinal titanium powder.
It has thus become possible to obtain titanium-tungsten targets having oxygen concentration as low as 900 ppm or less.
As has been described, research has been extensively conducted to reduce the oxygen content of titanium-tungsten target materials.
The above publications, however, do not disclose how the structures of titanium and tungsten constituting a target affect sputtering. That is, the publications do not disclose at all that an micro structure, particularly the presence of a titanium phase, is related to the occurrence of a particle phenomenon during sputtering which will be described below.
With recent higher density and thinner lines of electrode patterns of semiconductor products, even when the previously described titanium-tungsten target having low oxygen concentration is used for sputtering, large particles what is called "particles" are generated on a thin plated film as a result of the sputtering. This has given rise to a new problem of breaking electrode wiring.
A reduction in the oxygen content of the titanium-tungsten target alone does not eliminate the generation of the particles.
To solve such a problem, the inventor of the present invention has examined in detail the relationship between a target structure and the generation of particles, and found that large titanium grains are related to the generation of the particles. In other words, the inventor has ascertained that, when both titanium and tungsten are present, titanium having a light atomic weight is selectively sputtered, and tungsten grains, which are close to or contained inside the large titanium grains are scattered from the target material in the form of large diameter particles. This is one of the reasons for the generation of the particles on the substrate.